Normally, in known coffee machines of the type described above, when the dispenser cup is fitted to the sprinkler in the infusion position, the first piercing device pierces the sealing film of the sealed capsule inside the dispenser cup, and pressurized hot water is fed into the sealed capsule. The pressure and temperature combine so that the end wall of the sealed capsule, which is normally made of relatively thin thermoplastic material, is deformed outwards into contact with the second piercing device, which pierces it to allow the liquid coffee to flow out of the sealed capsule to the percolator spout.
In known machines of the type described above, the second piercing device is normally defined by a relatively large number of relatively thin, crochet-hook-shaped needles projecting axially from an end surface of the dispenser cup.
In actual use, given their relatively large number and irregular shape, the needles have been found to produce tears in the end wall of the sealed capsule, thus resulting in poor control of infusion flow from the sealed capsule and in dreg spillage. Poor infusion flow control is further compounded by the relatively large number of needles used—which, being so many, fail to pierce the sealed capsule simultaneously—and by the relatively large infusion flow passage formed by each needle in the end wall of the sealed capsule.